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Misc 44 The value of ∫_0^1▒tan^(−1)⁡((2𝑥 − 1)/(1 + 𝑥 − 𝑥^2 )) 𝑑𝑥 is equal to (A) 1 (B) 0 (C) −1 (D) 𝜋/4 Let I=∫_0^1▒tan^(−1)⁡((2𝑥−1)/(1 + 𝑥 − 𝑥^2 )) 𝑑𝑥 I=∫_0^1▒tan^(−1)⁡[(𝑥 + (𝑥 − 1))/(1 + 𝑥(1 − 𝑥) )] 𝑑𝑥 I=∫_0^1▒tan^(−1)⁡[(𝑥 + (𝑥 − 1))/(1 + 𝑥(𝑥 − 1) )] 𝑑𝑥 Using 〖𝑡𝑎𝑛〗^(−1) 𝑥+〖𝑡𝑎𝑛〗^(−1) (𝑦)=〖𝑡𝑎𝑛〗^(−1)⁡[(𝑥 + 𝑦)/(1 − 𝑥𝑦)] ∴ I=∫_0^1▒[tan^(−1) (𝑥)+tan^(−1) (𝑥−1)] 𝑑𝑥 I=∫_0^1▒〖tan^(−1) [−(𝑥−1)] 〗 𝑑𝑥+∫_0^1▒〖tan^(−1) (−𝑥) 〗 𝑑𝑥 Using The Property, P4 : ∫_0^𝑎▒〖𝑓(𝑥)𝑑𝑥=〗 ∫_0^𝑎▒𝑓(𝑎−𝑥)𝑑𝑥 ∴ I=∫_0^1▒〖tan^(−1) (1−𝑥) 〗 𝑑𝑥+∫_0^1▒〖tan^(−1) (1−𝑥−1) 〗 𝑑𝑥 I=∫_0^1▒〖tan^(−1) [−(𝑥−1)] 〗 𝑑𝑥+∫_0^1▒〖tan^(−1) (−𝑥) 〗 𝑑𝑥 I=−∫_0^1▒〖tan^(−1) (𝑥−1) 〗 𝑑𝑥−∫_0^1▒〖tan^(−1) (𝑥) 〗 𝑑𝑥 tan^(−1) (−𝑥)=−tan^(−1)⁡〖(𝑥)〗 Adding (1) and (2) I+I =∫_0^1▒〖tan^(−1) (𝑥) 〗 𝑑𝑥+∫_0^1▒〖tan^(−1) (𝑥−1) 〗 𝑑𝑥−∫_0^1▒〖tan^(−1) (𝑥) 〗 𝑑𝑥−∫_0^1▒〖tan^(−1) (𝑥−1) 〗 𝑑𝑥 2I=0 ∴ I=0 Hence, correct answer is B.

  1. Chapter 7 Class 12 Integrals
  2. Serial order wise

About the Author

Davneet Singh

Davneet Singh has done his B.Tech from Indian Institute of Technology, Kanpur. He has been teaching from the past 14 years. He provides courses for Maths, Science and Computer Science at Teachoo